topic Re: Back-button focus in EOS DSLR & Mirrorless Cameras

Thoughts on EOS 5D Mark III back-button focus

RobertTheFat — Sat, 05 Jul 2025 17:44:30 GMT

Last week I had an "optional" photo shoot at a civic event in our town, so I used the opportunity to experiment with back-button focus. I'd never used it, but a friend who's a sports photographer had told me how much he liked it (each of us has a 5D Mark III), so I set up the buttons and gave it a try.

Overall, BBF worked pretty much as I had expected; and while I didn't really notice any significant benefit for the kind of photography I do (landscapes, architecture, and events, mostly), I could see where it could be useful in certain circumstances. But one thing bothered me: When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.) I guess I can see the logic to it. With BBF it's assumed that that there's a high probability that you'll recompose, in which case a red square wouldn't necessarily mean that what's behind it is what was in focus. But I found it a bit annoying anyway. After all, you can recompose with shutter-button focus, and that doesn't make the red squares go dark. Is that really how it works, or am I missing something?

Re: Back-button focus

Waddizzle — Wed, 24 May 2017 22:35:45 GMT

You need to be pressing the BBF when you activate the shutter. It is sort of lik maintaining a half press on the shutter to maintain a focus lock in One Shot Mode.

The focus point is still reported in EXIF, because Lightroom has an add-in that can distinguish between when you're holding the button, and when you're not, although the info isn't spelled out in that fashion. It reports multiple states of focus lock.

One state indicates a focus lock, and AF point was the one you selected. Another state says focus locked, but you did not have the point selected, which is the case when you have released the BBF button when you activate the shutter.

Re: Back-button focus

ebiggs1 — Thu, 25 May 2017 13:31:16 GMT

Bob from Bean Town,

"I didn't really notice any significant benefit..."

Neither did or do I. Maybe it's because we are too old school as I don't use a lot of the newer functions available. I am currently content using with a camera that doesn't have all of them!

Re: Back-button focus

Ray-uk — Thu, 25 May 2017 14:11:51 GMT

They don't come much more old school than me, 70yrs old and been playing with cameras since I was 18. One day I might just get that perfect shot I keep trying for.

I wouldn't be without back button focus, it's the perfect way to separate focus lock from exposure lock.

I must admit there are a lot of other new functions I don't care for though.

Re: Back-button focus

ebiggs1 — Thu, 25 May 2017 14:28:22 GMT

I still shoot my F1n and I am just fine with it.

Re: Back-button focus

TTMartin — Thu, 25 May 2017 15:34:52 GMT

Instead of BBF, I reprogram the AF ON button to be AF OFF.

That gives me the ability to press the 'back button' when using AIServo and I need to temporarily suspend focus.

I find that the times I need to suspend focus are a lot less than the times I want continuous focus. So for me BBF would just mean having to press two buttons (back button and shutter button) most of the time. Where having the AF OFF button available just means I occasionally have to press two buttons (back button and shutter button).

To my knowledge all cameras that have an AF ON button allow you to reprogram it to AF OFF. I know the 40D/50D/6D/7D/7D Mk II for sure do.

Re: Back-button focus

Ray-uk — Thu, 25 May 2017 16:02:32 GMT

No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.

Re: Back-button focus

TTMartin — Thu, 25 May 2017 17:28:54 GMT

@Ray-uk wrote:
No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.

If you use BBF you have to keep pressing the back button for continuous focus.

So if you are shooting a sequence of action shots (moving subject) you have to press both the shutter and the back button at the same time.

As a sports and wildlife photographer I want continuous focus most of the time. I only want to stop focus on rare occasions. So I'm going to have to press two buttons most of the time, so on rare occasions I can remove my thumb and stop focus? Seems silly to me. Why would you want to have to press two buttons most of the time?

Re: Back-button focus

ebiggs1 — Thu, 25 May 2017 17:57:16 GMT

"No, cannot see the point of that."

......and here comes a MTF chart to prove it.

Re: Back-button focus

diverhank — Thu, 25 May 2017 19:10:46 GMT

@RobertTheFat wrote:
When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.)

This is interesting...I've been using BBF for years now. I had never paid any attention to the red squares and how they work but I can tell you recently I was doing a presentation on photography and needed a couple of pictures showing the red square focus and I used DPP and got the squares.

Granted I only grabbed a couple of pictures to do that and got the squares. I don't doubt depending on the settings, sometimes you don't get the squares. So at least for me, the squares are still there, using BBF. For these pictures, I did not recompose, if that's making any difference.

Re: Back-button focus

Ray-uk — Thu, 25 May 2017 19:12:28 GMT

@TTMartin wrote:
If you use BBF you have to keep pressing the back button for continuous focus.

So if you are shooting a sequence of action shots (moving subject) you have to press both the shutter and the back button at the same time.

As a sports and wildlife photographer I want continuous focus most of the time. I only want to stop focus on rare occasions. So I'm going to have to press two buttons most of the time, so on rare occasions I can remove my thumb and stop focus? Seems silly to me. Why would you want to have to press two buttons most of the time?

Yes, I see your point, as I don't do much action stuff I haven't had that problem but it is well worth considering.

Re: Back-button focus

diverhank — Thu, 25 May 2017 19:35:42 GMT

@TTMartin wrote:
@Ray-uk wrote:
No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.
If you use BBF you have to keep pressing the back button for continuous focus.

So if you are shooting a sequence of action shots (moving subject) you have to press both the shutter and the back button at the same time.

As a sports and wildlife photographer I want continuous focus most of the time. I only want to stop focus on rare occasions. So I'm going to have to press two buttons most of the time, so on rare occasions I can remove my thumb and stop focus? Seems silly to me. Why would you want to have to press two buttons most of the time?

TTMartin, I'm not sure I'm following you very well...I may learn something new after this... 🙂

The way I shoot birds is that I track and focus lock on the bird by AI Servo which means the focus button is continuously pressed. When I feel I got perfect everything, I press the shutter to take the shot. In the default, as you know, I'd have to half press the Shutter button to AI focus then fully press to take a picture. The primary reason I use BBF was that I don't want to inadvertently press the shutter button while doing continous focus (AI Servo) by traditionally half-pressing the shutter button. I tend to get overexcited and press the shutter a little too hard while I'm not ready. When I have only a second or two to shoot after waiting for hours, a mis-timed shutter trip can be disastrous when focus has not yet been achieved. It happened to me more than once and that was why I switched to BBF. I only press the shutter to take the shot and I don't need to press the focus button while taking the shots so I never press two buttons at the same time anyhow and if I did, it wouldn't matter.

Another problem with the regular shutter focusing scheme is it refocuses on you when you press the shutter to take a shot. I hate that in some cases. By using the BBF, I don't have to deal with this.

Re: Back-button focus

RobertTheFat — Thu, 25 May 2017 20:41:33 GMT

@diverhank wrote:
@RobertTheFat wrote:
When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.)
This is interesting...I've been using BBF for years now. I had never paid any attention to the red squares and how they work but I can tell you recently I was doing a presentation on photography and needed a couple of pictures showing the red square focus and I used DPP and got the squares.

Granted I only grabbed a couple of pictures to do that and got the squares. I don't doubt depending on the settings, sometimes you don't get the squares. So at least for me, the squares are still there, using BBF. For these pictures, I did not recompose, if that's making any difference.

Well, if not recomposing means that you didn't take your thumb off the button, I guess that's consistent with what Waddizzle said earlier. The camera abandons the red squares if you release the button because it assumes you've recomposed.

So one important difference between BBF and shutter-button focus, at least in one-shot mode, is that with BBF it can tell that you may have recomposed, while with SBF it can't. Does that make sense?

Re: Back-button focus

Waddizzle — Thu, 25 May 2017 23:17:50 GMT

@RobertTheFat wrote:
@diverhank wrote:
@RobertTheFat wrote:
When I edited the pictures in DPP 4, there were no red squares to indicate which AF points had achieved focus. (I was using the mode that divides the AF points into groups; and if any point in the selected group achieves focus, that's what's used.)

Well, if not recomposing means that you didn't take your thumb off the button, I guess that's consistent with what Waddizzle said earlier. The camera abandons the red squares if you release the button because it assumes you've recomposed.

So one important difference between BBF and shutter-button focus, at least in one-shot mode, is that with BBF it can tell that you may have recomposed, while with SBF it can't. Does that make sense?

Yes, I think I understand what you puzzling out. Maybe this helps. While DPP doesn't display the AF points if you're not pressing the BBF button, the data is still recorded. DPP just doesn't show it to you. This is what the LR Plug-in shows you.

Here's a closeup of the Legend.

The top state occurs when you lock focus in One Shot with BBF, and then recompose with your thumb off the button. The first state also occurs when you use AI Servo and lock on a subject.

The second state is what occurs when you hod the button when you activate the shutter. The third state is pretty much self-explanatory. The fourth state occurs when you never press BBF.

Re: Back-button focus

TTMartin — Fri, 26 May 2017 00:40:23 GMT

@diverhank wrote:
@TTMartin wrote:
@Ray-uk wrote:
No, cannot see the point of that. If you use back button for focus then in AI Servo just take your thumb off it and it stops, assuming of course you have also removed the focus operation from the shutter button.
If you use BBF you have to keep pressing the back button for continuous focus.

So if you are shooting a sequence of action shots (moving subject) you have to press both the shutter and the back button at the same time.

As a sports and wildlife photographer I want continuous focus most of the time. I only want to stop focus on rare occasions. So I'm going to have to press two buttons most of the time, so on rare occasions I can remove my thumb and stop focus? Seems silly to me. Why would you want to have to press two buttons most of the time?

TTMartin, I'm not sure I'm following you very well...I may learn something new after this... 🙂

The way I shoot birds is that I track and focus lock on the bird by AI Servo which means the focus button is continuously pressed. When I feel I got perfect everything, I press the shutter to take the shot. In the default, as you know, I'd have to half press the Shutter button to AI focus then fully press to take a picture. The primary reason I use BBF was that I don't want to inadvertently press the shutter button while doing continous focus (AI Servo) by traditionally half-pressing the shutter button. I tend to get overexcited and press the shutter a little too hard while I'm not ready. When I have only a second or two to shoot after waiting for hours, a mis-timed shutter trip can be disastrous when focus has not yet been achieved. It happened to me more than once and that was why I switched to BBF. I only press the shutter to take the shot and I don't need to press the focus button while taking the shots so I never press two buttons at the same time anyhow and if I did, it wouldn't matter.

Another problem with the regular shutter focusing scheme is it refocuses on you when you press the shutter to take a shot. I hate that in some cases. By using the BBF, I don't have to deal with this.

As far as inadvertantly taking a shot when you haven't achieved focus, that is a parameter you can set in the camera. If you set it right it won't take a photo without achieving focus in AIServo, just like wont in One Shot.

How to do you focus on birds flying towards you if you aren't pressing both the back button and the shutter button?

Those two are the last of about a sequence of 6.

As Art Morris says, 'when something happens press the shutter button'. I'd rather be able to do that then have to do a two button sequence.

By setting up the AF ON button to AF OFF you don't have to deal with the camera refocusing when you don't want it to as you can simply press the back AF 'OFF' button to stop it from refocusing. Times when I don't want continuous AF like focusing on a bird sitting on a branch through other branches of a tree, those then to be more laid back occurrences. I have the extra time to focus on the bird, either manual focus or slight focus and recompose, while pushing the back AF 'OFF' button.

FWIW, if you switched to AF OFF for action photography after learning about the AF OFF option you wouldn't be the first. I know of a couple of dedicated BBF users, who switched after learning about AF OFF.

BBF is actually very old tech going back to EOS film cameras (using the * ), AF OFF is something relatively new that only became available when Canon added the dedicated AF ON button. By providing a dedicated AF ON button for BBF they effectively outdated BBF, because with the AF ON button came option of reprogramming it to AF OFF.

Re: Back-button focus

TTMartin — Fri, 26 May 2017 01:17:42 GMT

Another example of tracking a bird moving towards the camera.

Glossy Ibis photobomb (near midair collision)*.

Re: Back-button focus

DaBrownCO — Sat, 10 Jun 2017 19:30:23 GMT

Hi Waddizzle,
I am new to BBF and just figured out myself why the auto-focus point wasn't showing up in Digital Photo Processor. The question I have: if you release the BBF, does it lock on the original focus point. It seems to, but curious. Thanks.

Re: Back-button focus

Waddizzle — Sat, 10 Jun 2017 20:47:12 GMT

@DaBrownCO wrote:
Hi Waddizzle,
I am new to BBF and just figured out myself why the auto-focus point wasn't showing up in Digital Photo Processor. The question I have: if you release the BBF, does it lock on the original focus point. It seems to, but curious. Thanks.

Yes. If you release the BBF, the lens ring will remaiin focused in its' last position. I wouldn't call it a "lock" though, because with many lenses you can manually override the AF simply by turning the "unlocked" focus ring.

If you figured out that the AF point is not displaying in DPP because you releassed the BBF, then you figured corrrectly. The record of which AF point locked focus, if any, appears to always be written to EXIF It just seems like DPP does not display the AF point when, and if, the AF system is idle at moment the shutter is activated.

Re: Back-button focus

DaBrownCO — Sat, 10 Jun 2017 21:58:44 GMT

Hi Waddizzle,

Thanks for confirming that the focus stays on the last focus point. I understand your point that it isn't really a lock. It's logical and also good to keep in mind.

Re: Back-button focus

Waddizzle — Sun, 11 Jun 2017 00:17:02 GMT

@DaBrownCO wrote:
Hi Waddizzle,
Thanks for confirming that the focus stays on the last focus point. I understand your point that it isn't really a lock. It's logical and also good to keep in mind.

Um, not quite the way I look at it. The focus does not stay on the last focus point. The lens remains focused at the last focused distance. The AF, focus points, are turned off and inactive, when you release BBF.

The subject that you had previously locked focused on could be in another part of the frame, or you could have turned arouind and be focusing elsewhere. The camera/lens combo will remain focused at the distance locked by the last active AF point. Distance, not focus point.

Be cognizant of the fact that all of this locked to the same distance can go out the window if your big zoom lens creeps on you.